In the field of 3D contents production, calibration techniques between a motion capture camera and a high-resolution video camera are absolutely essential techniques for producing high-resolution 3D contents for use in more vivid and realistic HD broadcasts and movies, by precisely composing computer graphic animation based on 3D motion capture data of a target object with moving video images that are taken simultaneously on the spot.
In the existing optical motion capture system, techniques for calibrating the motion capture camera and the video camera are classified into a calibration mechanism method which uses a separate camera calibration mechanism pre-manufactured for camera calibration, and a marker attachment method which allows the motion capture camera with a calibrating marker attached to the video camera or the background to recover 3D positions of the calibrating marker attached to the camera, thereby calibrating the cameras.
However, this calibration mechanism method or marker attachment method is restricted by the need of pre-manufacturing process or complicated installation procedure of the separate calibration mechanism or the calibrating marker for calibration of video camera. In addition, the calibration mechanism method or marker attachment method has difficulty since they must use different calibration mechanisms or change the marker attachment scheme depending on locations or conditions for photographing.
For example, the calibration mechanism method must use a large-sized camera calibration mechanism to get better observation even from a far distance for precise and stable camera calibration when a target object needs to be taken by the video camera in a wide motion capture area, and otherwise a small-sized calibration mechanism so as to let the calibration mechanism be seen in the near distance. Also, the marker attachment method has a complicated pre-manufacturing process of the calibrating marker, e.g., it must change the marker attachment scheme to have a larger marker-attached area if the motion capture camera and the video camera become more distant from each other, on the contrary, if those cameras become closer to each other, to have a smaller marker-attached area.
Meanwhile, calibration techniques for the motion capture camera and the video camera described above are not easy to apply when intrinsic parameters of the video camera are not pre-calibrated constants. For instance, the marker attachment method, by its own nature, can calibrate extrinsic camera parameters related to the spatial motion and rotation of the video camera, but it cannot calibrate intrinsic parameters of the camera related to high-resolution camera lens. Moreover, the calibration mechanism method also requires a separate calibration procedure to calibrate the intrinsic parameters.
Because of these problems, the conventional calibration techniques assume that the intrinsic camera parameters are all pre-calibrated constants. However, when it comes to the use of a high-resolution video camera, even a small change in intrinsic camera parameters does not guarantee precise calibration of cameras and therefore intrinsic camera parameters as well as extrinsic camera parameters must be certainly calibrated as variables.